Transistors are commonly used elements in integrated circuits. In a CMOS circuit formed by CMOS technology, an N-channel transistor and a P-channel transistor are usually included.
With the development of the semiconductor technology, a transistor comprising a back gate appears. Compared with a transistor comprising only a front gate or a gate stack, the transistor including a back gate has improved performance. A back gate contact realizing a desired electrical connection between the back gate and the other components in the circuit is one of the key components in the circuit.
In current semiconductor integrated circuits, SOI (Semiconductor-On-Insulator) technology gets more and more widely used. In a device formed by the SOI technology, in particular the ultra-thin SOI (UTSOI) technology, the back gate contact can help to control the threshold voltage and the short channel effect (SCE). Further, the back gate contact is also considered as a key component for the next generation of CMOS technology.
However, in the existing manufacturing flow for the semiconductor device or integrated circuits, the formation of the back gate contact may damage the structures already formed. For example, in the process flow of forming a device by the SOI technology, the formation of the back gate contact will probably damage a buried insulating layer or a buried oxide (BOX) layer in an SOI substrate. Hence, an additional protective layer (e.g., a nitride layer) is needed. Furthermore, the formation of the back gate contact requires an additional polysilicon filling. This makes the manufacturing process become particularly complex, and meanwhile increases the cost of manufacture.